Adaptive radiation of island plants: evidence from Aeonium (Crassulaceae) of the Canary Islands

Δ6-Desaturase sequence evidence for explosive Pliocene radiations within the adaptive radiation of Macaronesian Echium (Boraginaceae)

“…Xerophyllous ancestry at multiple nodes in the McClade optimization of the phylogenetic reconstruction (Fig. 3B), coupled with the predominant xerophylly of continental species and the large extent of xeric habitats in Macaronesia, lead us to hypothesize that speciation from early colonizers has been continuously occurring in dry environments (Jorgensen and Olesen, 2001). In summary, although ongoing xeric habitats have been in existence since the Canary Islands' origin, we propose that the advent of strong aridity in two events of the Pliocene (ca.…”

Paedomorphosis, Secondary Woodiness, and Insular Woodiness in Plants

“…Release from this selective pressure allows plants to complete their life cycles, and to exploit climatic moderation. Thus, rather than being consumed, the plants enjoy year-round growth, which eventually favors the evolution of increased woodiness and perennial growth forms (Carlquist, 1974;Jorgensen & Olesen, 2001). Supporting this idea is the fact that on islands where herbivores have been introduced predatory pressure has prevented the reproduction of some woody plants.…”

“…With greater longevity would come more flowers, which would allow a greater chance for cross-pollination by insect pollinators, which were then thought to be less common on islands (Carlquist, 1974;Givnish, 1998;Jorgensen & Olesen, 2001;Wallace, 1878). Unfortunately, this hypothesis has not been well supported.…”

“…A third hypothesis for the evolution of woodiness in insular plants was stimulated by the observation that islands have moderate climates (Carlquist, 1974;Jorgensen & Olesen, 2001). Island climates are either uniform throughout the year, or else have their climatic extremes moderated by oceanic influences.…”

Little interspecific pollen transfer despite overlap in pollinators between sympatric Aeonium (Crassulaceae) species pairs

“…several species of hybrid origin are known (Jorgensen and Frydenberg, 1999;Jorgensen and Olesen, 2001;Liu, 1989;Mort et al, 2002). Despite known isolation barriers like geographic, temporal or habitat isolation, the potential for hybridization in natural conditions is frequently reported for sympatric species with overlapping flowering times (Jorgensen and Olesen, 2001;Liu, 1989). Moreover, identical flower visitor species have been observed for several species of Aeonium (Hohmann et al, 1993), suggesting interspecific gene flow may be prevalent.…”